Control circuit



V. E. ROSENE CONTROL CIRCUIT Jan. 5, 1937.

Filed Jan. 50, 1935 2 Sheets-Sheet l /NVENTOR KEJQOSENE 5V ATTORNEY Jan. 5, 1937. v E, ROSENE 2,066,539

CONTROL CIRCUIT Filed Jan. 30, 1935 2 Sheets-Sheet 2 4 5:3 77 ATTORNEY 45 23 Vl/ENTOR 7 E 1 .ROSENE Patented Jan. 5, 1937 I UNITED STATES CONTROL CIRCUIT Victor E. Rosene, Montclair, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation oi New York Application January 30, 1935, Serial No.4,014

14 Claims.

This invention relates to control circuits and particularly to control circuits for adjusting the attenuation on telephone lines.

One object of the invention is to provide control circuits for adjusting the attenuation on a signal transmission line that shall compensate for the lag encountered when the direction of the attenuation control is reversed.

Another object of the invention is to provide a signal transmission line with attenuation control circuits that shall vary the attenuation on the transmission line according to the resistance variations of a pilot line and that shall conipensate for the lag encountered when a reversal is made in the direction of the attenuation control.

Another object. of the invention is to provide a signal transmission line with attenuation control circuits that shall vary the attenuation on the transmission line according to the resistance variations of a pilot line and that shall control the resistance of the pilot line to compensate for the lag encountered when a reversal is made in the direction of the attenuation control.

A further object of the invention is to provide a signal transmission line with attenuation control circuits that shall vary the attenuation on the transmission line according to the resistance variations of a pilot line, that shall insureagainst hunting action by controlling the resistance of the pilot line and that shall control the resistance of the pilot line to compensate for the lag encountered when a reversal is made in the direction of the attenuation control.

The transmission equivalent of a line varies according to the variations of a number of different conditions. One of the main causes of changes in the transmission equivalent is the change in temperature to which the line is subjected. Regulators are provided at repeater stations and terminal stations to compensate for the changes in attenuation on the line. In one form of regulator, attenuation networks are inserted in and taken out of the transmission line 0 according to the variations in resistance of a pilot line associated with the transmission line. In this type of regulator, trouble is often encountered by the lag produced when the direction of. the attenuation control is reversed. Regulators of the type under consideration wherein attenuation networks are selectively inserted in and Withdrawn from the line are disclosed in the patent to J. A. Coy et al., No. 2,017,654, October 15, 1935 and in the application of H. I. Bomnes,

Serial No. 716,934 filed March 23, 1934 now Patent No. 2,031,980 issued Feb. 25, 1936.

In attenuation control circuits constructed in accordance with the present invention, means are provided for so controlling the resistance of the pilot line as to compensate for the lag encountered when the direction of the attenuation control is reversed. The'means to compensate for the lag encountered when the direction of attenuation control is reversed may be combined with the means for preventing hunting action disclosed in the application of H. I. Romnes, Serial No. 716,934.

In the attenuation control circuits employed to describe the invention, a pilot line is associated with the transmission lines in a manner to be subjected to the same attenuation varying conditions as the transmission lines. The pilot line forms one arm of a bridge circuit which controls a galvanometer. The other three arms of the bridge circuit preferably comprise fixed resistance elements and a resistance element for balancing the bridge so that the galvanometer is operated in accordance with the variations in resistance of the pilot line. The galvanometer operates galvanometer control mechanism of the type disclosed in the application of H. I. Romnes, Serial No. 716,934.

The galvanometer control mechanism not only balances the bridge circuit after each operation of the galvanometer but also operates three commutator or contact rings. The contact rings not only control attenuation pads in the transmission line but also control the resistance of the pilot line to prevent hunting action at the time an attenuation pad is inserted in the transmission line or an attenuation pad is withdrawn from the transmission line. TWo relays are selectively controlled by the contact rings according to the direction of attenuation control. One of the relays is operated when an attenuation pad is being added to the line, and the other relay is operated when an attenuation pad is being withdrawn from the line. One of the relays is provided with an additional armature or switch arm for controlling a resistance in the pilot line to compensate for the lag encountered when the direction of the attenuation control is reversed. The galvanometer control mechanism'is provided with a number of moving parts which produce lag This lag interferes with the adjustment of the line attenuation when a reversal is made in the direction of the attenuation control. In the preferred control circuit, the lag above referred to is compensated for by controlling the resistance of a pilot line. This control of the resistance d: the pilot line to compensate for the lag cooperates with the resistance controlof the pilot line to insure against hunting action when an-attenuation pad is being inserted in. or withdrawn from the transmission line. r V.

' In the accompanying drawings:

Fig. 1 is a diagrammatic view of the galvanometer control mechanism employed 'in the attenuation control circuits;

r Fig. 2 is a diagrammatic ;view of attenuation; control circuits constructed in accordance with the invention;

Fig. 3 is a diagrammatic view of a momma tion of the invention wherein cammembersion the galvanometer control mechanism are employed to operate the lag compensating means;

Fig. 4 is a'diagrammatic view or another modi v fication of the invention whereinla'directional switch associatedwith the galvanometer control to operate the lag com mechanism is employed pensating' means; and

. Figs. 5 and 6 are diagrammaticviews offan-' other arrangement to compensate for. the lag encountered in'the attenuation control circuits.

Referring to Fig 2 of the drawings," a pilot line 1? is shown associated 'witha transmission line comprising conductors l and 2. The pilot line P" forms one arm of ac Wheatstone bridge circuit 3; The other arms of the bridge circuit 1 .3' comprise resistance elements R1,.R andRa.

An adjustable resistance element R4 which is varied by the galvanometer controlmechanism to balance the bridge vis connected between the resistance R3 and a resistance R5 in the pilot line armofthe'bridge. A battery 4 is connected to two opposite vertices of the bridge 13 and a galvanometer 5 is connected across the other two vertices of. the bridge circuit. Two. resistance elements Rs and Rs are provided for controlling the resistance of the pilot line" P to insure against hunting action. A resistance'R tion control.

,Referring to Fig. 1' of the drawings, the'galvanometer 5 is shown"controllinggalvanometer control mechanism 6. The galvanometer control mechanism 6 governed by the galvanometer' 5 comprises a 'U-shaped rocker arm 50 which is pivotally mounted at points 5|. ber 52" of. the galvanometer 5 is free to swing directly above a U-shaped supportin'g'member 53. which is attached to the rocker arm 50. An arm 54 secured to the'rocker arm50 engages a cam member 55 on a constantly rotating shaft 7 56. The shaft 56 is preferably connected to a motor 51 by suitable gearing 58. The gearing 58 also connects the motor 51 to a rotating paper roll 59.. The constant rotation of the cam member 55 serves to raise the rocker arm 50 at predetermined intervals. Preferably; the rocker arm 50 is operated approximately every eight seconds. A flexible arm 60 engages a second constantly rotating cam member 6| on the shaft 56. A cross arm 62 is pivotally mounted on the resilient arm. 6|] and carries a pair of shoes 63 which are adapted to frictionally engage a disc 1 64. The shoes'63 engage the disc 64 'for part of each revolution of shaft 56. The disc 64 by means of'a flexible connecting member 65 serves to control the movement of a recording pen 66. The :cross arm 62. terminates in a pair of projecting lugs 61 which are located in aposition '11, and 18;

. be mounted on the shaft 14;. The directional switchcomprises an arm -8ll:whi ch 'is adapted to engage one of two contact membersitl and 82 .the contact members BI and 82.

A pointer mem such that a pair of rotating cam members 68 on the constantly rotating shaft 56 will normally not engage them. A plate 69is fixed to the cross 7 arm 62 and carries apair of pins"). Pivotally mounted'arms H are heldinengagement with the pins lil by any suitable spring means not shown. Thearms H are provided with 'projections 12" positioned above'the point 52 otthe galvanometer 5.. V a

When the galvanometer needle or pointer 52 H will be given a movement of rotation to ro-' is deflected in one direction or the other, itwill pass "under one of the projections l l attached 1 tothe arms 1| and upon the rising of the rocker 1 arm 56"under contr ol of the cam member 55 on theconstantly rotating shaft56, one of the arms tate the cross arm'62 onits pivotal'support. V i

The rotative movement of the cross" arm 62 places one of. the projections 61' in the path of 'movement of one of the cam members 68. The

cam member68 upon engaging the projection .j

61: on the cross arm 62 moves the "cross arm back to its original position. Just before the cam member 68 engagesthe projection 61 on the cross arm 62, the cam member 6| will act to ,allowthe shoes 63 on the cross arm. 62 to frictionally engage the disc 64 and as the cross arm is given a, movement. of rotation, it will give a like movement of rotation to the disc 64ior controlling the recording needle or pointer 66.

resistance R4 and three commutator rings 16, A directional switch 19 -may'- also according to the-direction of rotation of the 1 shaft". The 'arm 86. is frictionallyconnected to the shaft 14 and follows the rotation of the i shaft 74 until engagement is made with one of The arm 86 engaging one of the contact members 8| and 82 indicates whether the resistance in the pilot 7 lineP is increasing or decreasing I Referring toFig. 2 of'the draWingsQthe commutator rings 76,,11, and l8 which are mounted on the shaft .14 of the galvanometer control mechanism 6 are shown in engagement .with

brush members I 8,,and 9 mountedon a switch arm in. The brushes 1, 8. and Bare insulated from each other and the brush 9 is grounded.

. The brush 1' is a cylinder or ball so as to bridge two' segments of the commutator ring 16 at definite positions when the commutator rings are c.

rotating in 'either direction. The brush 8 is preferably a cylinder or ball although it is not essential that it be so. constructed. The brush 9 is broader than the brushes 1 and 8 and. bridges two segments of the commutator ring 78 for a considerable movement of the commutator rings. The commutator rings l6; l7, andfi8 are mounted with the segments in the relative positions shown in Fig. 2 of the drawings. The three brushes 1, 8, and tare mounted in the positions relative to each other as shown in Fig. 2 of the drawings. Two relays Hand l2 are controlled by the commutator rings to place selectively a ground on conductors I3 and I4 which'arejconnected to the motor control mechanism l5. The motor control mechanism #5 is disclosed and claimed in the-patent to J. A. 2,017,654, October 15, 1935. The conductorsl3 and Min the system shown in Fig. 2'of the drawings correspond to the conductors 35 and 36 Coy .et al., No.

so The disc 64 is mounted on a shaft-14 which 1 also carries a'disc 15 supporting the slide wire 7 a latch member 20 engages a'bar 2I and holds attenuation control.

the relay in operative position. Thebar 2| is released when the latch 20 is operated by the release magnet I8. The relay I1 is provided with a bar 22 which engages a latch 23 for holding the relay I! in operative position. The latch 23 is operated by the release magnet I9 to release the bar22.

Assume that the resistance of the pilot line P is such thatthe galvanometer 5 is balanced with the brush member 'I engagingthe contact segment 24 of the commutator ring I6 and the brush member 9 engaging a corresponding R segment of the commutator ring 18. In this position of the apparatus the relay II is operated by a circuit extending from ground through the brush 9, commutator segment R, right contact arm of the relay I2, winding of the relay II and battery to ground. Assume now that the resistance of the pilot line is decreasingwhich corresponds to movement of the commutator rings towards the left, as viewed in Fig. 2 of the drawings. When the brush member I bridges contact segments 24 and 25 of the commutator ring I5, ground is applied to the conductor I3 of the motor control mechanism through the left contact armof the relay I I. The placing of ground connection on the conductor I3 starts the motor control mechanism shown in the J. A. Coy et al. Patent No. 2,017,654 to add attenuation networks corresponding to one step to all the associated transmission lines. The relay I6which is operated by the ground connection on the conductor I3 locks up mechanically under control of the release magnet 8.

The operation of relay I6 short-circuits the resistance R6 by means of its left armature. The resistance value of the resistance member R6 is such that when it is taken out of the pilot line, the galvanometer mechanism assumes a new balance with the commutator rings I5, 11, and I8 moved towards the left, as viewed in Fig. 2 of the drawings, one-fourth of the distance between the centers of two contact segments on the commutator ring I6. In moving to the new position, brush member 9 breaks engagement with the commutator segment R and opens the operating circuit for the relay II. The release of the relay iI allows the relay I2 to operate over a circuit extending from ground through the brush member 9, commutator segment L, right contact arm of relay ii, winding of relay I2 and battery to ground. The operation of relay I2 at this time prepares a circuit for a later operation.

Upon release of relay II, armature 32 of the relay disengages the contact member 33for insetting the resistance R in the circuit of the pilot lineP. The resistance R is inserted in the circuit of the pilot line P at this time to compen'sate for lag in the galvanometer control mechanism in case there is a reversal in the The resistance value of resistance R is such that the galvanometer mechanism assumes a new balance with the commutator rings I6, 11., and I8 remaining in the position taken when the resistance member R6 was taken out of the pilot line. The eifect of inserting resistance R in the pilot line P was to take up the back lash or lag of the galvanomperforms no useful function at this time.

eter control mechanism. If the resistance of the pilot line P continues to decrease, the commutator rings 16, I1, and 18 continue to move to the left and before any further changein the attenuation network takes place the relay II will again be operated as described later to shortcircuit the resistance R. The galvanometer mechanism assumes a new balance again without changing the position of the commutator rings I6, 11, and T8, but with the back lash or lag of the galvanometer mechanism taken up in the opposite direction.

Assume now that the temperature affecting the pilot line P continues to decrease and therefore the commutator rings I6, I1, and I8 continued to move towards the left, as viewed in Fig. 2 of thedrawings. When the brush member 8 bridges commutator segments 29 and 30 of the commutator ring 11, a circuit from ground through the commutator segment 29, brush member 8, commutator segment 30, winding of the release magnet I8, and battery to ground,

energizes the release magnet I8 to release the relay I6. Release magnet I9 is also energized but The release of relay, I6 removes the short-circuit around the. resistance member R6. The galvanometer mechanism 6 then assumes a new balance with the commutator rings moved onefourth of a step to the right, as viewed in Fig. 2 of the drawings. A step is considered the distance between the centers of adjacent commutator segments on the ring 'IBQ As the resistance of the pilot line P continues to decrease and the segments continue to be moved towards the left, as viewed in Fig. 2 of the drawings, the brush member 9 finally breaks engagement with the segment L and allows relay I2 to release. The release of reIay IZ operates relay II by a circuit extending from'ground through the brush member 9, commutator segment R, right arm of relay I2, winding of relay I I, and battery to ground. The operation of relay II prepares a circuit for later operation. As the commutator segments continue to move towards the left, as viewed in Fig. 2 of the drawings, the brush member I finally bridges com- I mutator segments 25 and 26 tostart the motor control mechanism I5 and operate relay I6 to perform the functions already described. When relay II is operated by the circuit completed by brush member 9 and the commutator segment B, it will be noted that resistance R is taken out of the pilot line P prior to the adjustment of the line attenuation when there has been no reversal in the direction of the attenuation control.

Consider the apparatus in its former position and assume that the resistance of the pilot line P begins to increase and that the commutator segments begin moving towards the right, as viewed in Fig. 2 of the drawings. The brush member I is on contact segment 25, brush member 8 is on contact segment 29 and brush member 9 is on contact segment L. Under such conditions, relay I2 is operated by a circuit extending from ground, through brush member 9, commutator segment L, right armature of relay II, winding of relay I2 and battery to ground. When brush member 1 bridges contact segments 2-1 and 25, a ground connection is applied toconductor I4. The ground circuit for conductor I may be traced from ground through commutator segment25, brush member I, commutator segment Z-Land left armature of relay I2 to the conductor [4. This ground connection placed on conductor. l4 starts-the motor controlimechanism I5 tosubtr'act an attenuation network corresponding. to one step from all associated transmission lines; :Relay I! which is operated by a circuit extending from groundon-conduc'tor l4; locks. up mechanically'under control of release magnet I9. The operationof relay'l'lremoves the short circuitaround resistance memberRs by means, of its right contact arm. Release magnet l8 would beoperated at this time if relay IB were in operative position by a circuit extending from ground" on the outerright contact arm of relay l6, through the inner left contact arm of relay I1, winding of release magnet .lfl and battery-to ground for releasingrelay l6; Atthis time, .it is apparent that both the hunting and Rsiare cut into ground through the brush member 9,'commu as'viewed in Fig. 2 of the drawings.

tator segment R, right contact arm of relay I2,

movingtowards;the right, as viewed; in Fig! 2 of the drawings, due to increasing pilot line resistance the brush' member 8 bridges commutator. segments 28 and Z9; Theground connec- 7 tion from commutator segment 29 extends through brush member .8, commutator segment 28, winding of releasemagnet l9 and battery toground. The operation ofthe release magnet l9 effects the release of relay IT, The release, of V Ildlilg on elm rings. Cross arms 62 and lugs 6'! are metallic'and are so radjusted that when .the right lug 51 makes contact with the right relay llprestores the short circuit around the resistance member R5 which, due to the rebal-' ancing actionof the bridge, moves the commutator segments one-fourth step towards the left, At this time'the brush member 9 is on commutator segment Rand relay I l is operated;

V Re sistance" R is in circuit with the pilot line 7 P'wh'en the relay I2 is operated and relay H is releasedr Thus, it is apparent when a reversal is made the operation of the attenuation control of the transmission :line by reason of the resistance of "the pilot line Pincrea'singf instead of decreasing, that the resistance R is inserted in the pilot lineP to compensate for the lag of the galvanometer control mechanism. If the resistancein 'thepilot line is increasing anda reversal is made in the attenuation control mechanism, then the resistance R is short-circuited from the ,pilot line P. .Alth ough the re sistance R is shown as being controlled solely by relay ll, it is apparent that the control of said resistance maybe effected by. relay l2 if so desired in'which [case resistanceR would be short-circuited by contacts on relay, l2, when this relay is in the released position.

As soon as the'pilot line resistance continues a to increase and the commutator rings 16, .11, and

18 continue to move towards the right, as'viewed in Fig 2*of the drawings, the. brush member 9 breaks engagement with the. commutator segment R, relay ll releases and;re1'ay I2 is operated. The circuit for operating relayl2 ex- 'tends from ground, through thebrush member 9, commutator segment L; right armature of releftlug 63 and vice versa;

of relay 34;

lay H, winding of relay l2 and battery to ground. a

' a When brush member 1 bridges thenext two adjacent commutator segments of commutator ring- 16, ground is again applied to the conductor. M for operating the motor control mechanism l5 to subtract attenuation pads from the line corresponding to one. stepfThe ground circuit on conductor l4 operates relay I! as above set forth.

' The above cycle of operations continues according to the resistance variations in the pilot line.

tion of operation of the attenuation control p detailed description of such apparatus will not begiven again when reference is made'to Figs.

3, 4, and'5. Moreover, like parts in Figs. 3, 4,

and 5 to those shown in Fig. 2 of the drawings, have been indicated-by similar reference characters.

Referring "to Fig. 3 of the drawings, resistance R which compensates. for the lag encountered 7 when a reversal ismade in the direction of. the attenuation controlis controlled by the galvae nometercontrol rnechanism- 6 shown in Fig. '1 of the drawings. 'A"relay:34 provided with two 7 armatures 35 and 36 isselectively operated aci cording to 'thepmovement of the cross armtl. which carries the lugs 61. Cams B8 are metallic and} insulated from shaft and each other.

Contact'to rotatinglcams 68 is effected by brushes cam 68, the left lug cannotmake contact with If relay 34 is in operative position, as shown in Fig. 3 of the drawings, resistance R is included in series with pilot line P. If relay 34 is released, armature 35 thereof short circuit sresistance R.

If the resistanceof -pilot line Pis decreasing,

cross arm 52 is given a clockwise movement of rotation as viewed in Fig. 3 of the drawings so that the left lug 61 engages the leftgcam 58. When the left. lug Bl engages the left cam 68,

'a circuitiscompleted for short-circuiting the winding of relay 34 so as to insure the release P is increasing and". the galvancmeter control mechanism 6' is operated to withdraw an attenua- 7 tion pad from the, transmission 'line,.cross arm 7 of armature 35 of relay 34 removes the short circuit across resistance R. The operation of armature 36 completes a holding circuit from battery 31 for relay 34. 7

.In the above manner'resistance R is controlled by relay fidtdcompensate for the lag of the galvanometer control mechanism 6 when a re- If the resistanceof the pilot line versal is made in the idirection of control. If

the galvanometer control mechanism has been operated by increasing resistance in the pilot line and the pilot line starts to decrease, then resistance R. is short-circuited from the pilot line. A reverse operation takes place and the short circuit across resistance R is removed if the galvanometer control mechanism has been controlled by decreasing pilot line resistance when the resistance of the pilot line starts to increase.

Referring to Fig. 4 of the drawings, a modification of the invention is illustrated wherein relay 34 which controls resistance R is controlled by a directional switch I9. The arm 8!] of the directional switch 19 is mounted on the shaft 14 of the galvanometer control mechanism 6. The arm 80 is frictionally connected to the shaft 14 and follows the rotation of the shaft until engagement is made with one of the contact members 8| or 82. If the resistance of the pilot line is decreasing then shaft 14 is rotating in a direction to move arm 80 into engagement with contact member 82 to establish a short circuit around relay 34 and insure the release of relay 34. When relay 34 is released, the armature 35 short-circuits resistance R as above set forth when reference was made to Fig. 3 of the drawings. If the resistance of pilot line P is increasing, then galvanometer control mechanism 6 is operated to rotate shaft 14 so that contact arm 80 engages contact member 8|. When arm 80 engages contact member 8|, a circuit is completed from battery 31 for operating relay 34. Upon operation of relay 34, armature 35 opens the short circuit around the resistance R and armature 36 completes a holding circuit for relay 34. The holding circuit for relay 34 is maintained until arm 80 is removed into engagement with contact member 82 to short-circuit relay 34. The operation of relay 34 is the same as above set forth when reference was made to the modification shown in Fig. 3 of the drawings.

Referring to Figs. and 6 of the drawings, a modification of the invention is disclosed wherein the lag of the galvanometer control mechanism 6 is compensated by mechanical means. The three commutator rings I6, 11, and 18 shown in Fig. 5 of the drawings, are provided with brush members 40, 4|, and 42. The brush member 40 which engages the commutator ring 16 essentially consists of two brushes 45 and 46 set closely together with the spacing between them determining the amount of the reduction in the lag. The brush member 42 is also in the form of a double brush but the spacing of the parts of the brush member 42 is not important except that the width of the brush must be greater than the width of the two brushes 45 and 46.

In describing the operation of the lag compensating means disclosed in Fig. 5 of the drawings, particular attention is called to Fig. 6 which discloses an enlarged portion of the commutator ring 16. Adjacent to the commutator ring 16 is shown a scale 44 which divides each step of the mechanism into ten parts. Assume that the resistance of the pilot line P is decreasing and that the commutator rings 16, I1, and 18 are given a movement towards the left, as viewed in Fig. 5 of the drawings. When the center of the gap between segments 24 and 25 shown in Fig. 6 of the drawings reaches position 24.5, brush members 45 and 46 (equivalent to brush member 40 in Fig. 5) bridges the commutator segments 24 and 25. At this time a circuit is completed from ground through commutator segment 25, brush 40, commutator segment 24, and armature of relay II to conductor l3 which is connected to the attenuation control mechanism [5. The attenuation control mechanism I5 is operated to change the attenuation pads in the line by one step and then to stop automatically. Ground on conductor I3 also operates relay I6 which looks up and short-circuits resistance Rs. Commutator rings 16, 11, and 18 are moved towards the left, as viewed in Fig. 5 of the drawings by one-fourth step which causes brush 42 to rest on an L segment of the commutator 18. When brush 42 disengages commutator segment R of the commutator ring 18, the circuit operating relay H is opened and relay ll releases. When relay H releases, relay [2 operates. A further decrease of pilot line resistance causes commutator rings l5, l1, and 18 to move to the left until brush member 4| bridges contact segments 29 and 30 which operates the release magnet l8. Relay l6 releases and inserts resistance Rs in the pilot line circuit. The gel-- vanometer mechanism rebalances and moves the commutator rings 16, I1, and I8, one-fourth step to the right, as viewed in Fig. 5 of the drawings.

If the resistance trend of the pilot line should change and start increasing, commutator rings 16, TI, and 18 would move towards the right, as viewed in Fig. 5 of the drawings. For any value of pilot line resistance, the commutator segments should arrive at the same position when moving towards the right as viewed in Fig. 5 of the drawings as when the segments were moved to the left previously. This is accomplished, as shown in Figs. 5 and 6, by separating the portions 45 and 46 of brush 40 a distance equal to the lag plus the separation between segments on commutator 16. The separation between all segments on commutator 16 is uniform. In Fig. 6, the lag compensation is shown equal to onetwentieth of a step. When a reversal of pilot line resistance takes place so as to cause the commutator rings I6, 11, and 18 to move towards the right, the lag in the galvanometer control mechanism prevents the commutator rings 16, 11, and 18 to move immediately after the reversal takes place. After the lag in the galvanometer control mechanism is taken up the segments 24 and 25 of commutator ring 16 moves towards the right as viewed in Fig. 6 of the drawings and shown in broken lines. When the center of the gap between segments 24 and 25 reaches position 24.45, the brush 40 bridges these segments. The contact between segments 24 and 25 is therefore accomplished one-twentieth step before reaching position 24.5 which compensates for the lag of the galvanometer control mechanism.

Modifications in the circuits and in the arrangement and location of parts may be made within the spirit and scope of the invention and such modifications are intended to be covered by the appended claims.

What is claimed is:

1. In combination, a pilot line subjected to resistance varying conditions, galvanometer mechanism, means for operating said mechanism according to the variations in resistance of said line, control means operated by said mechanism for governing the resistance of said line, and electrical means for compensating for the effect on said control means by the lag in the operation of said mechanism upon reversal in the operation thereof.

and forming an arm of said bridge circuit, galvanometer mechanism, means for operating said mechanismaccording .to the variations in resistance of said line and unbalance of said bridge, means operatedby said mechanism for rebalancing the bridge circuit, and electrical means for compensating for the efiect on the means operated by'said mechanism of the lag in the operation of said mechanismupon reversal in the operation thereof. b

I 3. In a gain control circuit for a transmission line, a pilot. line subjected to the same attenuation varying conditions as the transmission. line, control means comprising a galvanometer mechanism operated in a' forward and in a reverse direction according to the resistance variations of the pilot line to control the transmission line attenuation, and electrical means for compensating for the efiect on said control means of the lag in the operation of said galvanometer mechanism upon reversal in the operation thereof.

4. In a gain control circuit for a transmission line, a bridge circuit, a pilot line subjected to the same attenuation varying conditions as the transmission lineand forming an arm of said bridge circuit, galvanometer mechanism, means for operating said mechanism in a forward and in. a reverse direction according to the forming an arm'of said bridge circuit, galvanometer mechanism, means for operating said mechanism according to the variations in resistance of said line and unbalance of said bridge, means operated by said mechanism for rebalancing the bridge circuit, and means for varying the resistance of said pilot line upon reversal in'the opera-' tion of said mechanism to compensate for the lag in the operation of the mechanism.-

6. In again control circuit for a transmission line, a pilot line subjected to the same attenuation varying .conditions as the transmission line,

v control means comprising a galvanometer mechanism operated in a forward and in a reverse direction according to the resistance variations of the pilot line to control the transmission line attenuation, and means for varying the resistance of the pilot line to compensate for lag in the operation of said galvanometer mechanism upon reversal in the operation thereof.

'7. In combination, a bridge circuit, a pilot line subjected to resistance varying conditions and forming an arm of said bridge circuit, galvanometer mechanism, means for operating said mechanism according to'the variations in resistance of said line and unbalance of said bridge, means operated by said mechanism for rebalancing the bridge circuit, and means for inserting. resistance in said pilot line upon reversal in the operation of said mechanism when operating in one direction and for withdrawing resistance from said pilot line upon reversal in the operation of said mechanism when operating in an opposite direc'tionto compensate for lag in thejoperation of the mechanism. a r

8. In a gain control circuit for a transmission line, a bridge circuit, a pilot line subjected to the 9. In combination, a transmission line, a pilot line subjected to the same. attenuation varying conditions as the transmission line, galvanometer mechanism, means for operating said mechanism in a forward and in a'reverse direction according to the variations in resistance of said pilot line, two relays selectively operated by said mechanism for controlling the transmission line attenuation, and means comprising a resistance element controlled by one of said relays for varying the pilot line resistance upon reversal of said mechanism to compensate for the lag in the operation of the mechanism. 7

10. In combination, a transmission line, a bridge circuit,a pilot line subjected to the same attenuation varying conditions as the transmission line and forming an arm of said bridge circuit, galvanometer mechanism, means for operating said mechanism in a forward and in areverse direction according to the variations in resistance of said pilot line and unbalance of said bridge, means operated by said mechanism for rebalancing said bridge circuit, two relays selec tively operated by said mechanismfor controlling thetrans'mission line attenuation, and means ;comprising a resistance element controlled by one of said relays for varying the pilot line resistance upon reversal of said mechanism to compensate for the lag in the operation of the mechanism.

11. In a gain control circuit for a transmission line, a bridge circuit, a pilot line subjected to the same attenuation varying conditions as the transmission line and formingan arm of said bridge circuit, galvanometer mechanism, means for operating said mechanism in a forward and in a reverse direction according to the variations in resistance of said pilot line and unbalance of said bridge, means operated by said mechanism 'for rebalancing said bridge circuit, two relays selectively operated by said mechanism for controlling the transmission line attenuation, a resistance element, and means operated by one of said relays for inserting said resistance element in the pilot line upon reversal in the operation of said mechanism when operating in one direction and ,for withdrawing said resistance from the pilot line upon reversal in the operation of said mechanism when operating in an opposite direction to compensate for lag in the operation of the mechanism.

12. In combination, a transmission line, a pilot line subjected to the same attenuation varying conditions as the transmission line, galvanometer mechanism, means for operating said mechanism in a forward and in a reverse direction according to the variations in resistance of said pilot line to control the transmission line at- 751 tenuation, and means comprising a switch operated by said mechanism for varying the pilot line resistance upon reversal of said mechanism to compensate for the lag in the operation of the mechanism.

13. In combination, a transmission line, a bridge circuit, a pilot line subjected to the same attenuation varying conditions as the transmission line and forming an arm of said bridge circuit, galvanometer mechanism, means for operating said mechanism in a forward and in a reverse direction according to the variations in resistance of said pilot line and unbalance of said bridge, means operated by said mechanism for rebalancing said bridge circuit and for controlling the transmission line attenuation, and means comprising a switch operated by said mechanism for Varying the pilot line resistance upon reversal of said mechanism to compensate for the lag in the operation of the mechanism.

14. In combination, a transmission line, a bridge circuit, a pilot line subjected to the same attenuation varying conditions as the transmission line and forming an arm of said bridge circuit, galvanometer mechanism, means for operating said mechanism in a forward and in a reverse direction according to the variations in resistance of said pilot line and unbalance of the bridge, means operated by said mechanism for rebalancing said bridge circuit and for controlling the transmission line attenuation, a resistance element, and means comprising a switch operated by said mechanism for holding said resistance element in the pilot line when the mechanism is operated in one direction and for holding said resistance element out of the pilot line when the mechanism is operated in a reverse direction to compensate for the lag in the operation of the mechanism.

VICTOR E. ROSENE. 

